Servomotor



0t.141947.` vs-,MMAEQDOX x 2,429,189

sERVoMoToR Filed Aug. 29, 1944 s sheets-sheet 1 OctY 14, 1.947; s. -v.4MADDOX sERvoMOToR Filed Aug. 29, 1944 3 Sheets-Sheet 2 oct; 14,- 1947. iS V, MADDOX 2,429,189

SERVOMOTOR Filed Aug. 29, 1944 3 Sheets-Sheet 5 .5 GEAR- 102 K k.AUTOMATIC M GEAR j@ la 1p/mum Patented Oct. 14, 1947 UNITED ctrl-CEM2193??? snRvoMo'roR England, assgnor to HL. M1 1i,

Londen? England' Application August 29. 134.4, Serial. Nte-4551,71@

in Great Baai 5 anims.

This invention relates to hydraulic servornotors of the type in whichthe servopiston is moved to one or other of tvvo'alternative endpositions under the control of an operating valve actuated by apressure-sensitive device,

The operating valve is normally constituted Aby a piston valve vwhichcontrols' pressure and exhaust connections to the s ervocylinder toeiect movement of the servopis-ton from its one end position to theother when the load on the pressure-sensitive device exceeds a givenlimit, and

to return the servopiston to its original-.position servomotor isarranged to Vchamge :the gear ratio of the blower of anaircraft .engine.under `the control of a Adev-ice sensitive-to atmospheric .pressure. Ioaccelerate the movement of the piston it has been proposedto introducebetween the servocylinder and the .operating piston valve a piston-typeshuttle .valve which Vfollows-the Inove- -ment of the operating pistonvalve and, when displaced from eitherof -its end-positions, is effec.-tive to provide an unrestricted iiow o f pressure fluid to one end .ofthe servocylinder Vand an unrestricted flow of exhaust tluid from theother end.

The invention provides an hydraulic servomotor of the above type,comprising a pair of `con.- duits communicating respectively withopposite connections to pressure'and exhaust which are reversible by theoperating valve, and means conlLtrolled lby 'the servopiston, andarranged to .be operated thereby, .after :Preliminary slow moveence ofsaid restricted 110W, to establish during aportion atleast of theremainder .of the stroke of the piston v`pressure and exhaustconnections to the cylinder which permit of unrestricted i'low ofpressure iiuid, `thereby enabling the `Vservopiston-to travelathighspeed.

AIn the preferred form ofthe invention the pis.- ton is constituted by arotatable vane r`and the -20 It iS,

A4.0 ends of the cylinder .and providing restricted flow .4.5 mentVthereofin .either direction under the influn January ,1., i9 (ci.1lele-Fifi) a the servomotor @meri sL a Spindle' are@ t9 the vana-'and'having nl c ,annee @maurice 'ne ,respectively with the 1p rti 'ns ftnenursing 0e opposite Sides' fof the vara Sleye' yell/.Q f: rounding the'.spindle and termed' .with treasure apparatus, .Fies- 12;4 ar.

011 the lines VeVii; F

*.Fia "7 iiS .a view vSim `ar t0' `fifegfbilt taken 'tlirf'ligh thexhausi Paris' Qf the sleeve valve .in5- tead 0f .the Pressure ,Portsandfshowine the parts v 'eigrmefpverrde ,mechanismuiiable .for Op ation.flight Like reference Characters lindiciate' "like" vparte inmanente:Th'appaitatu (S iF'gS# i .mit i, i @esente efe-hersslots 26, 2T thepurpose of which will be explained later. The depth of the slot is lessthan the amplitude of movement of the vane.

At low altitudes the piston valve I2 occupies the position shown in Fig.in which a restricted flow of pressure liquid is allowed through theport I8, partially masked by the upper land 28 of the valve, to theupper end of the housing 20, the' lower end of the housing beingconnected to ex- Y haust via port I9 (partially masked by the lower land29 of the valve) and p'ort I5. Under these conditions the servo vane 2|is in thebottom position'shown in Fig. 2, and the blower is in M gearfor low altitude andmoderate supercharge.

As the altitude increases and the capsule stack I0 expands, the pistonvalve I2 will move down until it assumes the position shown in Fig. 7.Pressure oil is then able to pass through the port I9V to the undersideof the vane 2 I, andthe upper end of the vane housing' isconnectedtoexhaust via the ports I8, I6. The vane consequently travels to the upperend of its housing to change the blower over to S gear for high altitudeand full supercharge. i

For a given changefof4 altitude, which is represented by a smalldisplacement only of the piston valve I2, only a very smallamount of oilis passed from the piston valve to the vane chamber. This would causethe vane to travel very slowly from its one end position to theother'fand this movement would be too slow to give .satisfactoryoperation of the blower clutches and would also cause excessive wear. Aswillbe later explained, however, the vane, by eiecting lrelativemovement between its spindle 22 and the sleeve 24 provides unrestrictedflow of pressureoil tothe vane chamber,'in such'a way as to' Ygive aslow-initial travel of thevane, followed by rapid passage-over the majorpart of its journey and finally a slow travel into itsr ends position.The piston valve I2 therefore Amerely selects the V'direction in whichthe vane will travel and gives it a start on its way, thevanethereafter'automatically speeding up to give a quick gear change and atthe same time resetting the mechanism in readiness for the reversetravel when selected.

Itrwill be noted that the lands 28, 29 are wider than the ports I8, I9,.which provide the alternative connections from pressurev andexhaust tothe opposite ends of the vane housing, the lands being of sufficientwidth to vprovide a-lag in the operation of the change speed gear,represented as so many feet of altitude on either side of the nominalchange speed height. This is necessary to prevent the control fromhunting when the aircraft is iiying at about the norminal change "speedheight. s

As an alternative to using a piston Valve of the two-land type, asillustrated in Figs. 1-7, a valve having a single land can be used asshown in Figs. 8 9. The porting of the sleeve I3 is exactly the same butthe land ||2 controls the flow of pressure iluid from port I4. The twoports I8 and I9, the connections of which to the vane housing are inthis case reversed as compared with Figs. 5 and 7, port I9 leading tothe top of the housing and port I8 to the bottom oi the housing, are

not obstructed at all, and the two exhaust ports I6 are alternatelyopened and shut by the body of the piston valve as shown. Thus in Fig. 8the valve I2 is in the up position, corresponding to M gear, andpressure is directed to the upper side of the vane through port I9,while in Fig. 9 the valve I2 is in the down position corresponding to Sgear, and pressure is directed to the underside of the vane through portI8. The single land |I2 and the width of the annular gaps each side ofit, will of course be suitably dimensioned to provide the desired lag inoperation of the change speed gear.

The altitude at which the gear ratio is altere is varied in accordancewith the selected boost as follows. The pilots lever (not shown) bywhich the boost is selected is coupled to an arm 30 lixed to avertically rotatable shaft 3| carrying a cam 32. This cooperates with afollower 33 supported on a sleeve 34 carrying a claw 35 which pressesagainst theupper end of the capsule stack. When another boost pressureis selected, the shaft 3| is rotated, thus causing the cam 32 to rotatethe sleeve 34, and so vary thev datum of the capsule stack I0 andtherefore the altitude at which the blower gear ratio will be changed tomaintain the particular boost pressure selected.

A manual over ride lever is provided, by lwhich the datum of the capsulestack I0 can be altered to obtain S ratio on the ground, if so desiredfor checking purposes.

If required the manual override linkage may be re-arranged to permit theselection of M or S gear when in iight. One method of achieving this isillustrated in FigflO. The Vlever 95 is in this case removed from sleeve34 leaving the variable datum system otherwise unaltered. This is notshown in Fig. 10 being identical with that of Fig. 1 apart from theremoval of the lever 95. The piston valve I2 is provided with anextension |00. An override lever |04 is pivoted at some suitable xedpoint |03, one end'l02 of the lever being 1ocated in a gap IIlI in theextension |00 of the valve, and the other end |05 being connected to alever (not shown) in the cockpit. The gap I 0I is wider than the leverend |02 thus allowing free movement of valve vI2 when lever |04 is inthe automatic position. If the lever end |05 is placed in either M or Sgear position, the end |02 will contact the appropriate face of valveextension |00, thus moving the valve up or down. This will set theblower gear change mechanism in motion as already described.

One reason for overriding the 'blower gear change mechanism in iiight,is to prevent a gear change occurring when taking oi from an aerodromeat an altitude corresponding to any particular gear change height.

The automatic speed-up mechanism for the vane will now be described withreference to Figs. 2-7. The spindle 22 is formed with two axial channels36, 31 which are permanently in communication with the upper and lowerportions of the vane housing respectively through the agency of theextension slots 26, 2l. The sleeve valve has a pair of pressure ports38, 39 and a pair of exhaust ports 4I), 4|. It is movable under thecontrol of the vane between two alternative end positions, in which itis held by engagement of a ball 42, pressed by a spring43, with one orother of two notches 44 (see Fig. 6) The movement of the sleeve valve iseffected, shortly before the vane reaches the end of its stroke, byengagement of the vane with one or other of the end faces 45 e of theaperture 25. Thus in Figs. 4 and 6 the vane is shown near the end of itsmovement into .position to select S gear, and is abutting against theupper end face l5 of the aperture.

On completing its journey, the vane moves the sleeve valve from theposition shown in Fig. 6 to that shown in Fig. 7, the ball @2 thenengaging the upper notch 411 to hold the sleeve valve in thisalternative position.

Starting from the position of Figs. Zand 5, when the piston valve l2 has.been depressed Suniciently'to reverse the pressure and exhaustconnections to the vane housing, a restricted flow of pressure'oil isprovided through the port I9 to the undersurface of the vane, and theupper portion of the housing is connected to exhaust through the portsi8 and I6. The vane therefore starts :to travel vslowly towards the upposition.

Under these conditions the sleeve valve 2li has its pressure port 39 incommunication with the pressure inlet l via a duct Q7, while thepressure port 38 is closed by the portion t8 of the casing in which thesleeve valve revolves, as shown in Fig. 5. Also (see Fig. 1) the exhaustport 40 is open to exhaust via ducts 4S, 49 and the exhaust port il isclosed by the portion 5l) of the casing. When the vane has movedsufficiently to bring the channel 3l in the spindle 22 into registerwith the port 39 (see Fig. 3) an unrestricted lio-w of pressure oil isprovided to the undersurface of the vane, via the port 39, channel 3land extension slot 2l. At the same time this initial movement of thevane has brought the channel 33 in the spindle into register with theexhaust port til (see Fig. 3) and there is unrestricted flow of oil fromthe upper side of the vane to exhaust through the extension slot 26,channel 33, port it and ducts 49, GG. The vane therefore begins totravel rapidly until it reaches the position shown in Figs. 4 and 6.that is, with the vane in contact with the upper face 45 and with thechannels 35 and 3l still in register with their respective ports 40 and39. The vane and sleeve valve 24 now move as one part, thus maskingpressure port 39 with the portion of casing at 5l, (see Fig. 5), andopening port 38 to duct 4l. At the same time the vane has carried theexhaust port lll in sleeve 2li, out of register With duct [i9 (Fig. 7)causing it to be masked by the portion of casing at 52, and has openedthe exhaust port di to duct 39. It will be understood that although thepressure port 38 and exhaust port lil have been registered with ducts diand di! respectively, there will be no flow of fluid through them as theports 38 and lll are closed on their inner sides by the body of spindle22 (see Fig. 4). The mechanism has now re-set itself to travel in thereverse direction when selected by the valve l2 to do so. The vane 2l,spindle 22 and sleeve valve 24, however, continue to move in the samedirection to contact a xed stop formed by the end of housing 2e, thisextra movement being necessary to provide an adequate seal between thevarious ports. It is during this extra movement that the vane movesslowly under the influence of a restricted flow of fluid from the valvel2.

When the piston valve l2 operates again to reverse the pressure andexhaust connections to the vane, the latter will begin to rotate slowlyin the anticlockwise direction until the channels 36, 3l are broughtrespectively into register with the open pressure port 38 and the openexhaust port 4I. The vane will then speed up, and move fast until therecesses come out of register with their respective ports, whereupon thevane will slow 6. up again and iinally return thes-leeve valve -24 tothe-v position -s-hown in Fig. -5. v

It wifll'be 4understood'however that the hydraulic servomotor accordingto the invention has many other useful applications besides its -use forYchanging the -gear ratio of the blower. The amplitude of the slowstarting and nishing movements can of course be adjusted by asuitable-selection of the size and location of the ports Ain the-sleevevalve. v

' The illustrated vane-type servomotor with rotaryshuttle valve has Atheadvantage over the known piston-type -motor with piston-type shuttlevalve that a large amplitude of angular move- -ment of the vane is,obtainablev without the need off ii-tting additional par-ts. vTheangular movemen-t of the vane,- as opposed yto the rectilinear movementof thepiston-ty-pe servomotor, is a considerable advantage from theYpoint of View of installation, particularly in the case of aero enginecontrol units.

What I claim as my invention and desire to secure by Letters Patent is:

1. An hydraulic servomotor comprising a servopiston, a cylinder housingsaid servopiston, an operating valve for electing movement of theservopiston to either of two alternative end positions in its cylinden'apressure-sensitive device for actuating said operating valve, a pair ofconduits communicating with opposite ends of the cylinder and providingrestricted flow connections to pressure and exhaust which are reversibleby said operating valve, and means, controlled by the servopiston andarranged to be operated thereby after initial slow movement thereof ineither direction under the influence of said restricted flow, forestablishing during at least a portion of the remainder of the stroke ofsaid piston pressure and exhaust connections to the cylinder whichpermit of unrestricted flow of pressure fluid.

2. An hydraulic servomotor, comprising a piston constituted by arotatable vane, a housing surrounding and shaped to t the vane, anoperating valve for effecting movement of the vane to either of twoalternative end positions in its housing, a pressure-sensitive devicefor actuating said operating valve, a pair of conduits communicatingrespectively with opposite ends of said housing and providing restrictedflow connections to pressure and exhaust which are reversible by saidoperating valve, a spindle lixed t0 the vane and having axial channelscommunicating respectively with the portions of the housing on oppositesides of the vane, and a sleeve valve surrounding the spindle and formedwith pressure and eX- haust ports arranged to be brought selectivelyinto register with the channels in the spindle, after preliminary slowrotation of the vane and spindle from either end position, to establishthrough the channels said unrestricted pressure and exhaust connectionsfor moving the vane at high speed.

3. An hydraulic servomotor as claimed in claim 2, in which the sleevevalve is arranged to be rotated by the vane, when the latter approachesthe end of its stroke in either direction, between alternativepositions, in which alternative pairs of pressure and exhaust ports inthe sleeve cooperate with the channels in the spindle to direct theunrestricted flow of pressure fluid to the appropriate side of the vane.

. 4. An hydraulic servomotor as claimed in claim 2, in which the sleevevalve is arranged to be rotated by the vane, when the latter approachesthe end of its stroke in either direction, between alternativepositions, in which alternative pairs of pressure and exhaust ports inthe sleeve cooperate with the channels in the spindle to direct theunrestricted ow of pressure Huid to the appropriate side of the vane andin which said sleeve valve is formed with an aperture through which thevane projects, the aperture being of the same width as the vane but ofdepth less than the stroke of the vane, said aperture being formed atits ends with extension slots each aiording communication With one ofthe channels in the spindle in all positions of the sleeve valve andspindle.

5. An hydraulic servomotor as claimed in claim 2, comprising a springplunger for engaging notches in the sleeve valve to hold the latter inits alternative position.

STANLEY VICTOR MADDOX.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Number

